Contemporary mobile devices are often able to run on power supplied by chargeable electrical storage components like for example a chargeable battery. Usually the chargeable battery is internal to the mobile device and not visible from the outside. Some of these mobile devices, like for example laptop computers, may be configured for a dedicated connection to a power socket like the wall AC power sockets found at home and in offices, usually by means of a charger transforming the AC voltage to a lower DC voltage suitable for the mobile device. When such a connection to an external power supply is established, the chargeable battery is charged. On the other hand, these mobile devices are also often able to connect to other devices, often to several at the same time, via various wired connections which are often serial connections. Examples include the universal serial bus (USB), which comes in different varieties and versions like Hi-Speed USB, On-The-Go USB (OTG USB), Hi-Speed On-The-Go USB (Hi-Speed OTG USB) and even Wireless USB, as well as IEEE 1394 also known under the FireWire brand name. These serial interfaces allow not only exchange of communication data between the connected devices, but also the supply of electrical power. The electrically supplied power is used on the one hand for powering the serial connection itself, but may also be further received by any device connected which is not supplying the electrical power for the serial connection. Thus, a device connected in such a way to other devices supplying electrical power may use this electrical power from the connection for its operation as well as for the charging of its chargeable batteries. This is also known as “charge and play” functionality. A dedicated charging device may also connect to a mobile device to be charged via an adapter using such a serial connection. In fact, some mobile devices only provide such a serial connection interface for charging and have no separate dedicated interface.
Often, however, if a mobile device detects that it is connected via one of its serial data interfaces and the device it is connected to is supplying power, then it will use this electrical power for its operation as well as for charging its chargeable batteries. Usually at least one of the devices connected is required to supply the electrical power for the serial connection. Thus when only mobile devices running on their respective chargeable batteries are connected, then the one that is not supplying the power to the serial connection will start charging its chargeable batteries, not knowing that the device supplying the power is not connected to a wall socket power supply. Consequently, it is a problem that in such a situation the mobile device will just charge itself off the other's battery, potentially even causing the battery of the device supplying the power to be drained completely.
Published United States Patent Application 2007/0046268 A1 discloses a terminal connectable to an external device with a battery that receives power from the external device via a connection, a determination unit that determines whether the external device is a dedicated power supply apparatus on the basis of a detection result and a controller that controls charging of the battery on the basis of a determination result.
It is therefore an object of the present invention to be able to communicate to a mobile device receiving power from a connection that the power supplied to the device via the connection should be used sparingly.